Wine is the most loved beverage across the world and a popular accompaniment with food. The popularity of wine in India has started growing rapidly. Wine is the fermented product of the grape. Because crushed grapes contain all that is needed to create wine, ancient wine producers simply allowed nature to take its course. As time went on, people realized that by intervening at certain times, they could make a wine with more predictable characteristics. Grape cultivation is one of the most remunerative farming enterprises in India. Grapes can be eaten raw or they can be used for making wine, jam, juice, jelly, vinegar. Delicate wine grapes are generally produced in frost free and moderate temperature environments. Thousands of grape varieties are grown all over the world; the wine grape varieties represent only a fraction of them. The colour, size, phenolic distribution and acidity of grapes give each wine its own characteristic. Wine quality is affected by the factors such as soil, climate, viticulture and wine making techniques. Wine quality is dictated mainly by the grapevines, not by the winemaker. Wine must be slightly aged to be drinkable. Grape production, linked with wine processing has provided the much-needed impetus for the growth of the wine industry. Indian government plays a crucial role in the current phase of Indian wine industry, supporting the current momentum amongst others through financial assistance and market protection. Gradual reduction of import duty levels will no doubt lead to increasing competition through imports, but will on the longer term result in a competitive industry that is able to export its top quality products to overseas markets.
Some of the fundamentals of the book are wine quality, mold and mold complexes associated with grapes, grape aroma components, soluble solids in winemaking, the molds and yeasts of grapes and wine molds, yeasts of grapes and wine, by-products of fermentation, chemistry of fermentation and composition of wines, outline of red wine making, stuck wines, white table wine, sparkling wine, vermouth and flavoured wines, cider and apple wine, plum wines in Europe, berry wines in pacific coast states, cherry and plum wines in pacific coast states, pomegranate wine from concord grapes, pineapple wine, pear wine, wine from oranges, grapefruit wine, wine from dried fruits, Swiss research on fruit juice fermentation honey wine (mead), etc.
This book provides a complete detail on all aspects of Wine production like describe the varieties of wine available, its manufacturing process, bottling and storage of wine, quality control in wine making and many more. It is hoped that this book will be very resourceful to all its readers, students, scientists, technocrats, existing industries, new entrepreneurs and all those who are related to wine making.
Composition of Grapes
The character and quality of a
wine is determined by (1) the composition of the raw materials from
which it is made, (2) the nature of the fermentation process, and (3)
the changes which occur naturally, or are made to occur, during the
post-fermentation period. This chapter considers the composition of
grapes and the factors influencing it.
Amerine distinguishes physical
and chemical changes which occur during ripening. Obviously, however,
there is an intimate interrelationship between the two if changes in
volume occur, as they do.
The grape berry in its early
weeks is a tiny, green-colored, very acid pellet. Cell division and a
very slow berry enlargement continue for some time. Cell division
ceases about the time noticeable changes in berry size, color, and
The rate of increase in volume of
the berry may show a slight decrease during the period of seed
development, Fig. 1. Following this a very rapid increase in berry size
occurs so that in a few weeks the tiny berry becomes a plump, sweet,
colored fruit. The period of most rapid increase in volume does not
exactly coincide with the start of ripening. Fig 1 indicates that the
increase in soluble solids precedes this period by about two weeks.
The fruit does not continue to
increase in size indefinitely. When the fruit has reached normal
maturity there is a rather abrupt cessation of cell enlargement and
under very warm conditions there may be a decrease in volume. Peynaud
suggest harvesting one week after the fruit reaches its maximum weight.
The decrease in weight occurs mainly by withdrawal of water from the
fruit to the leaves—especially during periods of soil moisture
deficiency. Poux also noted that increase in sugar content paralleled
increase in berry weight. The ratio grams sugar per gram/total weight
in grams was a constant for a given variety when the fresh weight was
at its maximum.
Within the berry there are
changes in the relative amounts of skins, seeds, and pulp during
maturation. The changes on a per cent basis and on the basis of grams
per 100 berries are shown in Fig. 2. On a per cent basis the pulp
increases from about 73 to 89 per cent of the weight while the per cent
seeds and skins decrease from about 13 to 4 and 8, respectively. On a
per berry basis the increase in the weight of pulp is more striking and
a slight increase in skin weight occurs. It should be noted that
separation of the pulp from the skin and seeds is difficult and subject
to manipulative and evaporation errors.
Another physical change which is
of practical importance is that in turgidity. Unripe berries are hard
and difficult to crush. As the fruit ripens there is an increase in
turgidity. During overripening the fruit shrivels and there is a loss
in turgidity—making the fruit again difficult to crush.
Another physical change occurs
when the grape is attacked by Botrytis
weakens the attachment of the skin to the flesh and makes the fruit
easier to crush.
Besides the increase in glycerol
and sugar there is a net decrease in malic and tartaric acids,
especially in tartaric. The effect on the acidity and its intensity
depends on the climate following botrytis attack. Gluconic acid is a
constant product of botrytis attack. Amounts of 0.50 to 2.50 gm. per
liter were reported in wines made from botrytised Bordeaux grapes.
Normal wines had only about 0.29 to 0.92 gm. per liter. Charpentié
suggested a minimum gluconic acid as a measure of the authenticity of
botrytised wines. Galacturonic and glucuronic acids have both long been
considered to be present in small amounts in musts and in larger
amounts in musts or wines of grapes attacked by Botrytis
reported little glucuronic acid in normal or botrytised musts but
considerable galacturonic acid.
The constant presence of
glucuronic and galacturonic acids in musts and wines help to explain,
the deficit of anions in the acid balance, the high dextro-rotatory
condition of certain wines and some of the unknown compounds that
combine with sulfur dioxide. For 100 mg. of free sulfur dioxide, 1
milliequivalent of glucuronic acid will combine with 2 to 3 mg. of
sulfur dioxide and 1 milliequivalent of galacturonic acid will combine
with 5 to 6 mg. of sulfur dioxide. It is difficult to control field
conditions to secure the optimum botrytis growth. Attack by other molds
or rains may cause some sugar loss. Even under the best conditions
considerable net sugar is lost by respiration—up to 30 per cent.
Dextrose is attacked more by the mold than levulose so the
dextrose/levulose ratio decreases.
The grape consists of a seed
(except for a few varieties), surrounding pulp and on enclosing skin.
The relative proportion of each of these and their composition changes
during maturation. The present concept is that the grape ripens from
the exterior to the interior, but there may be varietal differences in
this. The pulp near the skin is thus, throughout the season, lower in
acid and higher in sugar than that near the seed. Because of the
increasing proportion of the fruit in the intermediate pulp zone, its
composition dominates that of the total juice more and more as the
season advances. This is of some importance in measuring ripening
changes. In partially ripe or ripe fruit when the berries are turgid
the free-run juice is mainly from the pulp near the skin and will be
higher in sugar and lower in acid than the juice from the press. In
overripe fruit where both turgid and nonturgid fruit are present the
free-run may be lower in sugar and higher in acids than the press
juice. This is due to the lesser proportion of juice from near the
skin—and from the non-turgid riper fruit—in the press juice.
When whole grapes are pressed, as
in the Champagne region of France, the first juice to be higher in
sugar and lower in pH and in
titratable acidity than that of later pressings. This is summarized in
Table 1. Intermediate pressings were higher in acidity and lower in pH
than the first juice, apparently because more tartrate-buffered
material was present. Certainly few non-turgid berries are present so
this represents the first case noted above. In California where
shriveling is common the second case is more common.
The over-all changes in sugar,
total acidity, and pH are shown for two varieties which ripen in
mid-season and one which ripens very late in Fig. 3. During the more
rapid stages of ripening in the warmer parts of California the Balling
may increase 0.1º to 0.4º per day and for each increase of a degree
Balling the acidity may drop 0.05 to 0.15 per cent. When ripening
starts there is a continuous increase in per cent sugar in the fruit.
The two sugars present, levulose and dextrose, do not increase at the
same rate, as shown in Table 2. Dextrose is the predominant sugar in
unripe fruit while levulose is at least equal and often higher in ripe
and overripe fruit. Very little sucrose has been found in V.
more is found in V.
other native species.
The titratable acidity decreases
during ripening, whether expressed on a per berry or on a per cent
basis. Since the acids are translocated into the fruit from the leaves
the changes in acids occurring in the leaves during ripening are
noteworthy. Amerine report a continuous increase in malates in the
leaves. The tartrate content of the leaves, generally decreases
slightly during maturation.
Maturity and Quality
Quality is a subjective judgment
that depends on the degree to which the wine is satisfying and balanced
and reflects the character of the grape. It can be described in nine
categories: color (hue, strength, purity, and stability), aroma
intensity, vitality (purity), complexity, subtlety, palate strength,
length, balance, and longevity. Hue refers to the dominant color
wavelength, strength to the depth of color, and purity to the degree of
“off” or tawny tones. Intensity refers to the magnitude of aromas and
vitality to the quality and purity of those aromas. Complexity denotes
the harmony of wine components. Delicate, refined flavors, strength of
palate, length of finish and balance, or the entire intergration of the
wine, and longevity or conservation, are also important quality factors.
Quality components are largely
the results of fruit characteristics governed by the parameters shown
in Fig. 1. Overlaid on basic grape quality is the mark of the
winemaker, who can adjust grape growing and wine-making to emphasize or
mute aromas, flavors, and textures to produce a well-balanced,
integrated product. Wine styles differ bacause of the tremendous number
of variables in grape growing and in winemaking, as discussed below.
A clone is a population of plants
all of which are descendants by vegetative propagation of a single
parent vine. many grapevine cultivars may not be clones, but mass
selections. However, such a distinction may be academic. When a
mutation occurs in a dividing cell, all cells derived from that
individual cell carry that genetic change. All vines produced from the
mutant shoot constitute a clone, yet are similar enough to their mother
vine to have the same varietal name.Clonal variation can affect yield,
setting rate, growth, clusters per vine, berry size, fruit rot
susceptibility, and berry flavor components. The latter two are of
Variations in vineyard and
winemaking techniques likely obscure all but the most pronounced
effects of clones on wine style and quality. However, the
identification of superior grapevines within cultivars remains an
Climatologists recognize three
levels of climate: macroclimate or regional climate, meso- or site
climate, and micro- or grapevine canopy climate. Wine quality is
influenced by the mesoclimate, particularly temperature, during the
final state (stage III) of berry ripening. Jackson and Jackson have
divided grape-growing regions into two temperate zones: alpha zones
with mean temperatures between 9-15ºC (48ºF-59ºF) during stage III
ripening; and beta zones with mean temperatures greater than 16ºC
The best variety for any region
is one that matches the length of the growing season, so that
maturation occurs even during the coolest portion of the season. The
optimum choice of cultivars should allow for fruit maturity just before
the mean monthly temperature drops to 10ºC/50ºF. In warmer climates,
the length of the growing season easily allows for adequate fruit
maturity but results in fruit development during the warmest part of
Microclimate is determined by the
presence of plant cover. Grapevine leaves are the major cause of
microclimate variations; the presence of fruit, shoots, stems, and
permanent vine parts are less significant. In the sense that grapevine
canopy influences microclimate, it is under the control of the
Canopy microclimate components
include radiation, temperature, humidity, and evaporation. Berries
maturing in densely shaded canopy interiors are generally associated
with the following when compared with berries in open or exposed
canopies: (1) low total soluble solids, (2) high titratable acidity,
(3) high malate concentrations, (4) elevated pH, (5) high potassium,
(6) low proline, (7) high arginine, (8) low total phenols, and (9) low
anthocyanin concentration in red and high chlorophyll vs. flavonoid
pigments in white cultivars. These differences are due to exposure to
sunlight and heat (see Tables 1 and 2).
Sunlight can affect vine and
grape physiology through photosynthetic and thermal responses. The
amount of diffuse solar radiation reaching the interior canopy leaves
and fruit decreases geometrically as the number of leaf layers
increases, resulting in a reduction in photosynthetic rates. Varying
shoot numbers, reducing vine vigor, or adopting training and trellising
systems that divide canopies into separate, thin curtains of foliage
improve grapevine microclimate and enhance grape quality. For vineyards
already planted to conventional trellis designs, alternative methods of
decreasing canopy shade may be desired.
Canopy microclimate can be
improved with selected fruit zone leaf removal which can result in
reduced fruit rot incidence. Increased spray penetration, desiccation,
and reduction of evaporation potential will likely contribute to rot
reduction. For a review of grapevine canopy microclimate evaluation and
Although the precise contribution
of each factor influencing the terroir (or soil-plant environment) is
not known, experience suggests that a ‘good’ terroir encourages slow,
yet complete maturation. Seguin suggested that a desirable terroir has
adequate but not excessive nitrogen, the ability to moderate the
influence of heavy rain, especially after veraison, as well as to
moderate drought stress. The influence of soil on wine quality is
widely debated. Rankine concluded that soil composition is less
important than climate. Jackson reported that soil is known to have
several direct influences on plant growth by affecting moisture
retention, nutrient availability, heat and light reflecting capacity,
and root growth as a result of penetrability. Soils that help promote
excessive vegetative growth may negatively influence quality by
altering canopy microclimate.
Yield is an important economic
and production consideration. The majority of vineyards producing
quality wines tend to be those having low to moderate yields. Because
high yield may delay maturity, direct effects are not easy to measure.
The leaf-to-fruit ratio is considered to be an important factor
influencing fruit sugar and the other components. For example, McCarthy
found that potential volatile terpenes (PVT) were higher in low-crop
vines. Kingston determined that 15 cm2 leaf
area per gram of fruit was optimum for soluble solids production.
Yields can be estimated if both the average number of clusters per vine
and the average cluster weight is known. Cluster counts may be
determined on a vine-by-vine basis before bloom when they are easily
visible whereas cluster weights are determined on a shoot-by-shoot
basis near veraison when weights begin to stabilize.
Quality and Soluble Solids
Grape maturity assessment as well
as fruit quality is critical to the successful production of palatable
wines. Part of the grower’s payment for the fruit often is based upon
delivery of grapes at agreed-upon parameters: so care must be taken in
the maturity monitoring process. Traditionally, degrees Brix (ºB,
weight percent sugar in the juice) and titratable acidity (g/L of acid
in the juice) have been selected as the harvest parameters most
important in monitoring maturity. Because of the importance of fruit
maturity to ultimate wine palatability, field sampling of fruit must be
performed in an objective and statistically acceptable manner.
Amerine compared sample
collection techniques and reported that berry sampling can provide an
accurate and economical sampling technique. Theoretically, to be within
plus or minus 1º B with a probability level of 0.05 (95 out of 100
samples), two lots of 100 berries each should be examined. In cases
where one wishes to be within plus or minus 0.5º B 95% of the time,
five lots of 100 berries should be collected.
Berry sampling is difficult
because of the time required and variations in fruit chemistry. The
chemical composition of grape berries differs with their position on
the rachis, the location of the cluster on the vine, and the location
of the vine in the vineyard. However, properly performed berry sampling
can provide an accurate picture of the overall vineyard fruit
chemistry. Jordan recommend collection of berries from the top, middle,
and bottom of the cluster. Terminal berries on the rachis may be less
mature than other berries. Berry sampling in various locations on the
cluster may be significant in the case of larger clusters; but many
persons, sample by selecting berries only from the middle of the
rachis, a technique that may be acceptable in the case of varieties
with small clusters. Additionally, in a berry sampling procedure the
side of the cluster from which the berries are taken must be
randomized. One should avoid selection of fruit from ends of rows or
from isolated vines or those with obvious physiological or
morphological differences. Vine suggested an alternating-row method of
sample selection. Significant variations in soil type shading, and so
on, may play an important role in vine growth and therefore fruit
maturity. Ideally, sampling should be designed to reflect differences
in soil type, topography, and vine growth. For consistency, some
recommend that selected vines within each block be targeted for
Samples should be collected at
approximately the same time period each day. Jordan have made the
following sampling recommendations: (1) edge rows and the first two
vines in a row should not be sampled; (2) samples should be collected
from both sides of the vine; (3) for each row, estimate the proportion
of shaded bunches and sample according to that proportion. This
proportion may vary with the side of the row sampled because of
variation in leaf cover. Smart demonstrated that white and red grapes
exposed to direct sunlight may be as much as 8ºC and 15ºC,
respectively, warmer than the ambient air temperature. Such exposure
may have a dramatic effect on fruit composition. Kliewer summarizes
these differences in Table 1. As the table shows, a sampling technique
that does not consider the effect of exposure to the sun may not be
There is a natural tendency when
one is picking individual berries to select those with the most eye
appeal. These are often the more mature berries. Such bias in a
vineyard sampling technique may result in Brix readings that are as
much as 2º B higher than that measured by the winery after crushing the
entire vineyard load.
Most growers begin sampling fruit
several weeks prior to harvest. Initially, samples are taken once
weekly, with a shift to more frequent intervals as harvest nears. Brix
and titratable acidity are the traditional harvest parameters most
important in monitoring maturity. Recently, the importance of pH,
aroma, organic acid, etc., has been established.
Measurements of ºB, titratable
acidity, and pH, by themselves, may not be specific indicators of
physiological maturity or potential wine character and palatability.
These parameters will vary considerably, depending upon the season,
crop load, soil moisture, and so on. Maturity is clearly a
multidimensional phenomenon, and should be viewed on a relative rather
than an absolute basis.
There is considerable variation
in the definition of optimum maturity for a particular wine grape
variety. If maturity is defined as that point in time when the berry
possesses the maximum varietal character consistent with the type and
style of wine desired, then the assessment of varietal character is a
logical adjunct and extension of conventional definitions of maturity.
Further, the optimal maturity may vary somewhat with the style of wine
to be produced. Long lists the parameters she considers important in
affecting fruit development and maturity assessment, which are
summarized in Table 2. The relative importance of each parameter is
predicated upon the type and style of wine to be produced as well as
the ability of the vine to continue to mature the crop. Several of
these parameters are described in more detail below.
Molds and Yeasts of Grapes and Wine
Molds are of importance in wine
making, first, because of the damage they may do to the grapes before
or after picking and, second, because they often grow in empty wooden
cooperage imparting a moldy odor and flavor to the wine. They do not
grow in wine because of the inhibitory effect of the alcohol.
Yeasts of the genus Saccharomyces are
necessary in the fermentation of the must, but they and other yeasts
may cause the clouding of bottled table wines. The flor yeasts, which
represent a special group, are used in the making of Spanish sherries
and certain Jura French wines. Wild yeasts, such as the apiculate
yeasts and others, may be harmful to wine quality when they develop
during fermentation, although in some cases they may produce flavors
which give a distinct or unique character to the wines.
Classification of Microorganisms
The complete Classification and
description of the microorganisms of importance and interest to the
wine maker would be beyond the scope of this book. A brief discussion
of the more important forms only will be given.
Some of the fungi are saprophytes
and can utilize only non-living substances for growth; others are
parasitic and can attack living tissues. Examples of the former are Penicillium mold
and wine yeast.Saccharomyces cerevisiae var. ellipsoideus. Typical
fungal parasites are Botrytis
mold”) and oidium of
the vine (powdery mildew).
Fungi may be unicellular or
multicellular. Yeasts are higher fungi whose dominant form of growth is
unicellular. Certain other fungi are always multicellular in growth.
Still others may under certain conditions grow as one-celled organisms
and later on under changed conditions become multicellular.
This chapter deals with the
occurrence, morphology, and some other general properties of the yeasts
and molds of importance in wine production.
Molds are distinguished by the
formation of a mycelium. They differ from each other principally in
their methods of producing spores and conidia, but there are also
easily recognizable differences in the appearance of the mycelium and
in the nature of the chemical changes which they induce in media suited
to their growth. Variations in external and microscopical appearance,
however, are not always reliable for identification and classification
as the appearance is often affected profoundly by conditions of growth.
Primitive fungi form a mycelium without cross walls (non-septate), and
the mycelium is termed “non-septate” or “coenocytic.” These molds are
also termed Phycomycetes. The
other molds, or higher fungi, possess a septate mycelium.
Some molds form yeast-like cells
under certain conditions and may even induce feeble alcoholic
fermentation, as do some of the Monilia and Mucor molds.
Many genera, species, and
varieties or sub-species of molds have been described in the
literature. They are usually aerobic, although they have been
encountered as a feeble growth in bottled juices that have not been
Molds of the penicillium group
are most troublesome to the California wine maker. In the initial
stages of growth Penicillium is
white in appearance. Later, spores or conidia are formed in enormous
numbers and give a powdery appearance to the growth, which is blue,
green, or pink, according to the color and age of the conidia and the
age of the culture.
P. expansum, (formerly P.
the best known of the penicillium molds and the one responsible for
very great losses to fresh fruit shippers and fruit product
manufacturers. The asexual spores of conidia are spherical in shape and
are formed in great abundance upon upright hyphae or conidiophores. The
conidia are light and are carried by air currents. They are universally
distributed on surfaces and in the air.
This mold will grow on
practically all food materials exposed to the air, if the conditions of
moisture content and freedom from antiseptics permit the growth of any
microorganism. It prefers sugar-containing substances such as fruits,
fruit juices, jams, etc., but will also develop on such material as
moist leather or the moist inner surface of empty wooden barrels or
tanks. Any acid material affords a more favorable medium for growth
than does an alkaline or neutral medium. After early fall rains it
often grows in great abundance on cracked grapes rendering them unfit
for wine making. The taste of these wines is very unpleasant, and on
the basis of our experience very little is required to taint the wine.
“Corked” wines may also have Penicillium sp.
in the cork.
Growth is more abundant at
temperatures ranging from 59° to 75ºf. but will occur at temperatures
near freezing and slowly at temperatures of 95° to 98°F. It is known as
a “cold weather” mold.
The alcohol content of a wine,
influences its stability as well as its sensory properties. Wines are
taxed, in large part, according to their alcohol levels. Careful
monitoring of alcohol is important in stylistic wine production, as
well as in carrying out accurate fortifications and in formulation of
blends for bottling.
Microorganisms have varying
requirements for oxygen. At the two extremes are the microorganisms
that require oxygen, the aerobes, and those that cannot survive in its
presence, the anaerobes. Between these extremes are facultative
microorganisms such as the yeasts, which are metabolically equipped to
handle conditions where oxygen is either plentiful or limiting. Under
oxidative (aerobic) conditions where concentrations of utilizable
sugars are less than 3%, yeasts utilize the pathway outlined by the
solid line in Fig. 1. Glucose is converted to pyruvate via the
Embden-Meyerhott-Parnas (EMP) pathway (glycolysis) and subsequently to
carbon dioxide and water via the tricarboxylic acid (Krebs cycle) and
cytochrome oxidase pathways. Alternately, where oxygen is limiting, and
a fermentable carbohydrate source is present, fermentative metabolism
ensues, with pyruvate being decarboxylated to acetaldehyde and
subsequently reduced to ethanol. This fermentative pathway is outlined
by dashed lines in Fig. 1.
Anaerobiosis is not the only
condition that favors fermentatitive metabolism. Even under conditions
of relatively high oxygen, the presence of glucose at levels of more
than 5% inhibits
the activity of respiratory enzyme systems. This example of catabolite
repression is generally referred to as the “Crabtree” or “counter
Pasteur effect.” Under such conditions, fermentative rather than
oxidative metabolism is observed. As glucose levels drop, TCA cycle
enzymes are induced, and metabolism may shift from anaerobic
(fermentative) to aerobic.
The energy differences between
metabolic pathways are considerable. Anerobic metabolism yields only 56
kcal/mol of glucose, whereas aerobic metabolism (respiration) of this
sugar produces 688 kcal/mol.
The importance of carbohydrate
metabolism to the yeast is twofold. On the one hand, the cell is
provided with a source of utilizable energy in the form of
substrate-level phosphorylations involving adenosine triphosphate
(ATP). Secondly, a variety of intermediate carbon compounds are formed
in the process that are channeled into related biosynthetic pathways of
On an equivalent basis, glucose
has a much greater energy potential than the energy generated by
conversion of ATP to ADP. However, the importance of ATP lies not so
much in its endogeneous energy content as in its direct involvement in
energy-transfer reactions. The latter attribute resides in very
reactive phosphate anhydride linkages.
The free energy of hydrolysis for
ATP is reported as 7 kcal/mol, whereas for ADP and AMP the values are
6.4 and 3.0 kcal/mol, respectively. Therefore, ATP serves as an “energy
carrier” whereby the energy produced from biological oxidation is
harnessed (conserved) in ATP synthesis rather than liberated
immediately in the form of heat. As such, this stored energy is
available to drive cellular reactions requiring the input of energy.
For brevity, only the salient points of the EMP pathway will be
addition to glucose, the monosaccharide fructose is fully fermentable.
In this case, direct phosphorylation yields fructose-6-phosphate and
of the trioses, dihydroxyacetone-phosphate and
glyceraldehyde-3-phosphate, occupies a special position of importance
to the wine-maker—namely, in the formation of glycerol, which is
discussed in greater detail later in this chapter.
initial phosphorylation of glucose to form glucose-6-phosphate and
fructose to yield fructose-1,6-diphosphate utilizes two molecules of
ATP. Direct energy in the form of ATP is recovered at two locations in
the EMP pathway. First, the oxidation of 1,3-diphosphoglyceric acid to
3-phosphoglyceric acid is accompanied by phosphorylation of ADP. A
second molecule of ATP is recovered in the formation of pyruvate from
One molecule of glucose produces
two molecules of the triose phosphate, so a total of four ATP’s are
generated per molecule of initial sugar. Subtracting the two ATP’s
utilized in initial phosphorylation reactions, the pathway yields a not
gain of two ATP’s. To emphasize the dramatic differences in energy
yield between aerobic and anaerobic glycolysis, the major reaction
sequences are summarized in Table 1.
The nucleotide NAD+ is
reduced to NADH + H+ in
formation of 1,3-diphosphoglyceric acid. Because intracellular
concentrations of NAD+ are
low, the cell must regenerate this compound if metabolism is to
continue. Under aerobic conditions, reduced NAD is reoxidized in the
cytochrome oxidase system of the cell, yielding an additional six ATP’s.
In the fermentative met-abolic
mode, however, NADH + H+ is
reoxidized in the reduction of acetaldehyde to ethanol. Fifty-six (56)
kcal of energy (7 kcal/ATP) are potentially available in glycolysis,
when coupled to oxidative pathways. However, during fermentation only
14 kcal (two ATP’s) are produced. This amounts to a net efficiency with
respect to ATP production of only 25% in anaerobic glycolysis.
Fermentations may be described as
a series of redox reactions in which organic compounds (in this case
sugars) are oxidized initially, and, at a later point, their products
serve as terminal electron acceptors. Thus a fermentable compound must,
ideally, be at some intermediary stage of oxidation; and carbohydrates
fit this requirement. Furthermore, the end products and by-products of
fermentation (ethanol and organic acids) are, themselves, at an
intermediate stage of oxidation. As such, they may serve as reservoirs
that may be available to the organisms growing under oxidative
conditions (i.e., acetic acid bacteria).
In fermentation, acetaldehyde
formed by decarboxylation of pyruvate may also combine with sulfite to
form an addition product (Neuberg’s second form of fermentation), as
shown in Equation 2-1:
Thus the addition of large
quantities of bisulfite acts as a block, preventing acetaldehyde from
operating as an hydrogen acceptor for NAD. Under these conditions, the
triose dihydroxyacetone phosphate replaces acetaldehyde as a hydrogen
acceptor, resulting in formation of glycerophosphate in amounts
equivalent to the quantity of acetaldehyde bound. Hydrolysis of
accumulated glycerophosphate by phosphate enzymes then leads to the
formation of glycerol. It has been reported that NAD regeneration
occurs in this manner in the early stages of fermentation before the
concentration of acetaldehyde reaches the levels needed for alcohol
dehydrogenase activity. However, utilization of this pathway does not
provide the cell with energy.
Additional alcohols of importance
in winemaking include glycerol, methanol, and several 3- to 5-carbon
alcohols collectively known as fusel oils. These may, on occasion, be
important in sensory and regulatory considerations.
of Fermentation and Composition of Wines
Fermentation originally indicated
the conversion of grape juice into wine. It is now applied to a variety
of processes of anaerobic dissimilation of organic compounds by
microorganisms, by living cells, or by extracts prepared from them. It
is also used for certain aerobic microbial processes. Alcoholic
fermentation is but one of the many chemical processes which may be
classified as fermentation. Other industrial fermentations of
importance produce antibiotics, acetic acid (vinegar), citric acid,
butyl alcohol, etc.
In any dissimilation process
organic compounds of higher energy are converted to products of lesser
energy with the subsequent release of energy in the form of heat.
Dissimilation processes are therefore oxidation-reduction reactions
including: (1) addition of oxygen, (2) removal of hydrogen, or (3) loss
of an electron. In the usual process hydrogen from the donor is
transferred by a series of enzymes and respiratory pigments to a
reducible substance, the hydrogen acceptor. Atmospheric oxygen,
reducible compounds in the substrate or intermediate compounds may act
as acceptors. Aerobic processes involve atmospheric oxygen while the
other two types are anaerobic in nature. An important difference
between aerobic and anaerobic processes is that the former release much
larger amounts of energy.
The famous French chemist,
Lavoisier, in 1789 made quantitative studies on alcoholic
fermentation—one of the first such studies of a natural phenomena. In
1810 Gay-Lussac correctly reported the over-all reaction in the famous
equation which bears his name:
2C2H5OH + 2CO2
It became clear in the late
twentieth century that the Gay-Lussac equation represented only the
over-all process of alcoholic fermentation.
The relation of yeasts to the
process of alcoholic fermentation had been noted by many early
investigators. In fact the species name Saccharomyces comes
from the Greek sakcharos, sugar,
However, Liebig, the great German organic chemist, considered the
yeasts to be without significance in fermentation and the weight of his
authority halted progress in understanding the process until Pasteur’s
Pasteur’s work, even though he
did not clearly understand the nature of the process, established the
essential validity of the Gay-Lussac equation but also showed that a
variety of by-products were present which were not accounted for by the
equation. Among the common by-products are glycerol, acetic and lactic
acids, and acetaldehyde. Since Pasteur’s time many biochemists have
devoted their time to tracing the complex process from sugar to
alcohol, carbon dioxide and by-products. Fig. 1 indicates the general
scheme and accounts for glycerol as one of the byproducts.
Even though the variety of
by-products and the importance of the enzyme system were established
before 1900 it was not until 1913 that Neuberg developed the first
tenable scheme of alcoholic fermentation. Progress was rapid thereafter
leading to the present generally-accepted series of reactions, Fig. 1.
During the initial induction
stage the hexose phosphate is converted to a-glycerophosphate and
3-phosphoglycerate, since at first the entire sequence of reactions is
delayed because no acetaldehyde is present. Glycerol is produced
directly from the a-glycerophosphate. The
3-phosphoglycerate is transformed to pyruvate which is decarboxylated
As acetaldehyde accumulates it
becomes the hydrogen acceptor (in place of dehydroxyacetone phosphate)
and reacts with reduced coenzyme I (NADH) to produce ethyl alcohol.
During the stationary phase this process predominates and little
glycerol is formed. If acetaldehyde is not available (when removed by
sulfite, for example) the induction phase continues and glycerol is
produced. Most of the reactions are reversible.
In the presence of a high
concentration of sulfur dioxide in acid solution acetaldehyde, carbon
dioxide, and glycerol are the primary products and alcohol a
by-product. If the sulfite solution is alkaline acetaldehyde, glycerol,
alcohol, and carbon dioxide are all produced. Other types of
fermentation have been reported. The glycolytic sequence clearly shows
the complexity of the system. It also shows how glycerol, lactic acid,
and acetaldehyde may accumulate as by-products. The tricarboxylic acid
cycle (Krebs) which starts with pyruvate can explain by-products such
as succinic acid. For the glycolytic cycle note that no less than 22
enzymes are required plus both magnesium and potassium ions and six or
of Red Wine Making
The red, colored pigments of most
grapes are localized in the skins. Therefore, in the making of red
table wines the juice is fermented on the skins in order to extract
this color during fermentation. In the making of white wine, on the
other hand, the juice is fermented free of the skins, in order to
extract as little color and tannin as possible. As the cellar
operations differ somewhat in other respects the two wine types will be
considered in separate chapters.
There does not seem to be any
doubt that Cabernet Sauvignon produces the highest quality red table
wines yet made in this state. The grapes normally arrive at the winery
in excellent condition and ferment well. If fermented on the skins more
than 4 or 5 days, the tannin content may be high and the wines will
require longer aging. Both in California and Bordeaux there has been a
tendency to press early. This results in wines of less tannin and color
but earlier maturity. The best Cabernets may not mature until they have
had 10 or more years of bottle aging.
Pinot noir presents special
problems in California because it ripens very early in the season.
Also, it appears to favor a warm fermentation and in some cases, a
malo-lactic fermentation. There are, further, at least two clones—one
much less colored than the other. We do not believe the highest
possible quality has yet been achieved from Pinot noir in this state.
Both cask and bottle aging are recommended.
Zinfandel ripens unevenly and
great care in harvesting must be exercised. The best wings appear to
come from vineyards on the slopes of hills in regions II and III. In
regions IV and V bunch rot is a problem. Contrary to pre-prohibition
opinion the best Zinfandels profit by cask and bottle aging. We have
tasted excellent Zinfandels of 10 to 15 years of age.
Ruby Cabernet, because of its
high total acidity, should be used for red table wines only when grown
in regions IV and V. There does not seem to be any more rapid aging for
this variety than for Cabernet Sauvignon when produced by the regular
procedures from grapes grown in regions II or III. Wines produced from
grapes grown in regions IV and V appear to mature more rapidly.
Petite Sirah is highly subject to
bunch rot and sunburn. Grapes from regions II and III are most likely
to produce the best wines. The same is true of Refosco and Carignane.
Grenache produces the best red wines from grapes grown in region I.
Elsewhere they should be used for producing rosé wines.
Calzin has been extensively
tested for red table wines. It is deficient in color and, suprisingly,
exceedingly high in tannin. It is not recommended for planting or wine
making in this state. Barbera, because of its high total acidity, is
recommended for planting in region IV for use in blending.
As grapes approach maturity, they
should be tested frequently in order that they may be picked at the
proper stage of ripeness.
As the grapes are received, each
load should be tested for Balling degree. If the grapes are found to be
excessively high in sugar they should be used for making port wine or
for distilling material. The addition of acid is often indicated for
table wines. It is best to add the acid early in the history of the
wine; for example, at the time of transfer from the fermenting vat to
the storage tank. Tartaric acid is preferred in cases of low acidity
(below 0.6 percent).
For this reason, Balling (or
Brix) tests on the grapes should always be accompanied by titration of
the samples for total acidity. There is evidence to indicate that
acidification before fermentation results in better development of
bouquet and flavor than if it is delayed until fermentation is
complete. In fact, addition to the crushed grapes is probably the best
procedure, except for the unavoidable loss of some of the added acid in
the pomace. It is also desirable to follow the pH during ripening as
musts of high pH are unsuitable for making high quality table wines. A
pH meter is used for this determination.
In California harvesting is
usually done, often by contract, by crews of itinerant pickers who pick
several vineyards in succession. Short, curved knives or short-bladed
shears are used in cutting the bunches from the vines but picking
shears, such as used for table-grape harvesting, are preferable, as
they slash the fruit less and also permit easier cutting out of rotten
berries. Lug boxes holding from 45 to 55 lbs. of grapes have been used
for picking and for transporting the grapes to the winery in most
table-wine vineyards. However, small gondolas which can be moved
through the vineyard are becoming increasingly popular. The gondola is
taken directly to the winery. In
some of the large dessert-wine grape vineyards, the grapes, after
picking into buckets or lugs, are dumped into large steel-bodied,
hopper-like trucks (called gondolas) and transported long distances in
bulk to the winery.
This is objectionable from the
standpoint of sanitation and microbiology, for inevitably many of the
grapes are crushed in bulk transfer, with consequent fermentation and
contamination with fruit flies(Drosophila melanogaster). Fermentation,
bacterial growth, and volatile acid formation have then been noted in
gondola trucks where crushing was delayed. Less objectionable is the
practice of picking into moderate sized bulk containers which are
transported directly to the crusher. Economy dictates that as little
handling of fruit be employed as possible, consequently direct
harvesting into containers which can be mechanically dumped into the
crusher probably will be used in the future.
Lug boxes or picking buckets or
tubs should be clean; not moldy or vinegar sour. Washing and steaming
such containers during the vintage, especially after a rain, is
Only sound (not moldy, or
mildewed, or vinegar-soured) grapes should be taken by the pickers.
Some varieties develop a considerable quantity of second crop bunches
that ripen 2 or 3 weeks later than the main crop. If the main crop is
overripe, it is often desirable to pick the second crop along with the
first in order that the second crop will furnish much needed acidity.
On the other hand, if the grapes are not overripe, it is better that
the second crop be left on the vine to ripen. The Zinfandel usually
sets a good second crop which if picked with the first crop in a cool
region will make the must unduly acid.
White wines are not simply
colorless wines. They differ fundamentally from red wines in
production, composition, and sensory quality. Since they are not
produced by fermentation on the skins the tannin and extract contents
are lower. Whereas red table wines are usually dry or nearly so white
table wines may be very sweet, as with French Sauternes or the Auslese wines
White wines are usually more
delicate in flavor than red and, owing to the lack of tannin and
coloring matter, defects in taste and appearance are more apparent in
them. Red grapes are usually fermented in open vats, whereas white must
is preferably fermented for dry wine in covered tanks or casks. White
wine fermentations are usually allowed to run to completion in tank or
cask, and then the casks or tanks kept full until the first racking in
December. Clarification and bottling may take place in 6 to 24
months—the lighter (lower-alcohol) types being sold first.
However, in the making of bulk
standard wines in California some of the larger wineries ferment the
white must in open vats until the Balling drops to 0° before
transferring it to storage tanks for the after-fermentation. The
fermentation of white musts in open vats results in loss of bouquet and
flavor if there is a quality potential in the grapes employed.
The recommended varieties for
planting in California have already been listed. Some further comments
here regarding their enological characteristics seem desirable.
White Riesling is the variety
for Riesling wine if one can afford it. It is a shy producer, sunburns
easily, and requires a low fermentation temperature. In California it
is most often erroneously named Johannisberg (or Johannisberger)
Riesling but White Riesling is preferable. Sylvaner (Franken Riesling)
and the so-called Grey Riesling have little Riesling character, either
in this country or abroad. The Walschriesling (Italian Riesling) is not
grown commercially in this country and does not produce a Riesling wine
in the countries where it is grown (Italy and Yugoslavia) but its wine
is pleasant. The Emerald Riesling has a distinctive aroma, more
reminiscent of its muscat than its Riesling parent. Its tendency to
darken, as noted by Berg is a serious defect but its high acidity is a
more than compensating factor, especially in regions III and IV in
California where the warm climatic conditions lead to low acidity in
other varieties. The Sylvaner, Grey Riesling, and Emerald Riesling each
vinified separately and properly cared for have a place in our wine
industry if planted in the correct region. Because of their tendency to
darken musts of Grey and Emerald Rieslings should probably be well
settled before fermentation.
Chardonnay produces excellent
wines but is a poor producer. It should be fully matured before
harvesting if the characteristic ripe grape aroma is to be developed.
Ballings of 23° are desired. Another low producer is the
Gewurztraminer. However, its distinctive aroma makes it useful. Very
careful harvesting is necessary to secure sufficient maturity for
flavor but one must avoid low acidity and excessive sugar by too late
harvesting. Flora, a new release of the California Agricultural
Experiment Station is now being extensively tested as a supplement to
or replacement of Gewürztraminer.
Sémillon is one of the best
all-purpose varieties now available, if it is not overcropped and is
not picked too early. Picked in mid-season at Ballings of 22.5 to 23.5,
it is the basis of a good standard white table wine. At slightly higher
Ballings, even under California conditions, it can produce sweet table
wines. In years of early rainfall immediate harvesting is advisable to
prevent excessive botrytis rot.
Sauvignon blanc is an excellent
variety but must be mature if its wine is to have a characteristic
aroma. This means harvesting at a Balling of at least 22.5°.
Overcropping is possible and delays maturity. Wines from overcropped
vines also have less flavor. Some of the best white table wines of
California have been made from this variety.
For standard white wines French
Colombard, Folle Blanche Chenin blanc, and Veltliner are all useful.
Some rot may develop in Chenin blanc and Folle Blanche in rainy years.
Delay in maturity owing to overcropping is a fault of Veltliner. Still
under trial is Helena, a new and promising hybrid of the California
Agricultural Experiment Station. Aligoté is probably about as useful as
Not recommended for general
planting for white table wines are Trebbiano (Ugni blanc or St.
Emilion), Palomino (darkens), Sauvignon vert (low acidity), Green
Hungarian (thin, neutral wines), and Burger (thin but possibly useful
as a sparkling wine stock); or table grape varieties such as Thompson
The proper time of harvest varies
from variety to variety, region, season, amount of crop, and the
prospective use of the fruit. The only way to fix the time accurately
is to determine the maturity of the grapes in the vineyard as
outlined. For early-maturing, fruity, white table wines harvesting can
begin at 20° to 21° Balling. For richer more flavorful slower-maturing
wines harvesting may be delayed to Ballings of 22° to 23°. The acidity
and pH must also be considered. Wines of better flavor and keeping
quality and easier clarification are produced from musts with an
acidity of over 0.70 per cent (as tartaric) and pH of 3.3 or lower.
In California the white grapes
are preferably picked into clean lug boxes or aluminum tubs; carried to
the end of the row to be picked up by truck or conveyed into small or
large metal containers for transport to the winery. If the vineyard is
on a steep slope the boxes are moved by tractor-drawn sled which
delivers them to the truck. Increasing amounts of grapes are
transferred in the vineyard to small or larger gondola trucks. Where
the transfer is carefully made, the gondolas clean, excessive crushing
of the grapes avoided, and the movement to the winery rapid, the system
works well. However, it is difficult to transfer the delicate white
grapes long distances in gondola trucks without considerable crushing.
Harvesting directly into large metal containers which can be unloaded
by power lifts is also common. Similar systems using wooden tanks are
used in Europe, particularly in Germany.
Great care should be exercised in
picking in order to avoid moldy bunches, particularly late in the
season. In some European vineyards, Champagne, for example, each bunch
is inspected and if necessary, unfit individual berries are removed by
small shears. Such extreme care is not necessary or economically
possible in California; however, after early rains the bunches which
become moldy should not be picked for wine making.
The boxes or baskets should be
scrupulously clean and free of all mold.
Sherry is the most important
California wine type. Sweet
white wines of low acidity containing unfermented sugar readily develop
on exposure to air a peculiar characteristic flavor known as rancio (goût
de rance in
France). The excessive caramelized odor of some baked sherries is not,
a true rancio flavor.
There are three types of wine
sold under the name of sherry. The first is that of the flor sherries
of Jerez de la Frontera in Spain which owe their characteristic flavor
and bouquet to the growth and action of flor yeasts that develop on the
surface of the wine. Similar types are produced in Australia,
California, Canada, the Jura region of France, the Soviet Union, and
South Africa. The second type is California sherry that owes its-flavor
and bouquet to baking. This type resembles the wine of the island of
Madeira more than any other. The third type is that which is aged in
small cooperage for several years without flor yeast or baking. The
aged non-flor sherries of Australia and California are of this type, as
are some of the wines of Banyuls in the south of France and the
Prioratos of northern Spain.
Sherry, particularly if dry, is
used traditionally as an appetizer wine or cocktail hour beverage.
The origin of the California
baked sherry process is not definitely known. One might assume that it
began as an attempt by a California wine maker to produce wines similar
in flavor and bouquet to certain kinds of Spanish sherry. If so, the
attempt failed. It is known that some California sherry in the last
century was baked in glass hot houses in barrels or puncheons, heat
being furnished by the sun. Later, artificially-produced heat was
In Spain the Palomino is the
principal variety grown for sherry production. It is low in acidity but
the sugar content is very acceptable for sherry, when well ripened. It
is rather neutral in flavor and aroma and the wines darken in color
after production,. In California other white varieties available in
abundance are also used. These include the Thompson Seedless variety
(Sultanina) grown extensively in the San Joaquin Valley for raisin
production and for fresh shipment for table use; Malaga, an important
white table and shipping variety; Emperor, a shipping grape of light
red skin color and white juice; and the Tokay (Flame Tokay), a red
grape of white juice grown extensively in the Lodi area. In New York
and other eastern states labrusca varieties characterized by their
pronounced varietal flavor are used. By the Tressler method the foxy
flavor is partially eliminated.
In the making of baked sherry,
the grape variety is probably of less importance than in the making of
any other California wine, because the flavor and bouquet of the final
product depend chiefly on the baking process and other cellar
operations. However, varieties of marked flavor, such as the Muscat of
Alexandria, should not be used, because sherry should not possess a
Muscat varietal flavor.
The grapes for sherry making
should be well ripened, as the final acidity should not be as high as
for table wines and the corresponding pH value may be somewhat higher.
Berg made sherries of various pH values by acidifying new white wine
made from Tokay grapes, the adjusted pH values being 4.0, 3.8, 3.6,
3.4, and 3.2.
Experienced tasters gave the
sherry of pH 3.2 the highest score and those of 3.4 and 3.6 a score
that was a close second to that of pH 3.2. The sherry of pH 4.0 was
given the lowest rating. The chief defect of the Palomino variety is
its relatively high pH.
Some sherry is made from the
grapes sorted out at packing houses as unsuitable for shipping fresh
for table use. These grapes are usually sound, but early in the
shipping season may be lower in Balling degree and higher in acidity
than is desired. However, sherries made from such grapes may be useful
In the principal sherry producing
districts of the State the grapes are picked into large pans or lug
boxes and transferred to gondola trucks for delivery to the winery, or
are first placed in small gondolas which in turn are emptied into large
Sherry making in California is
usually a large-scale operation. The grapes are crushed and stemmed in
the same manner as for other wines. Garolla-type crushers and stemmers
described in an earlier chapter have superseded roller crushers and
To the crushed grapes sulfur
dioxide in the form of the gas from a cylinder of the liquid is added,
or potassium metabisulfite is used.
The crushed grapes are allowed to
drain and the free-run is pumped to fermenters. They are large, usually
of 60,000 gallon capacity or even larger. In smaller plants concrete
vats or redwood tanks of 10,000 to 20,000 gallons are used. The drained
crushed grapes are generally employed to produce fortifying brandy. A
starter of fermenting must from another fermentation or of must
fermenting with pure yeast is usually added to the juice.
During fermentation, it is
customary to artificially cool the must to maintain the temperature
below 85°F. Ten of 19 plants surveyed stated that 80°F. is a more
Usually the must is fermented dry
or to a low sugar content. A small amount of sugar is considered
desirable during baking, but is often added later in the form of
angelica or fortified sherry material of high sugar content. In a
survey of Martini 11 of the 16 cellars fortified at —1º or lower
Balling, one at 0º Balling, and two “when dry.”
and Other Dessert Wines
In the preceding chapter the
production of sherry was discussed. The other principal fortified
dessert wines are port, angelica, Malaga, Madeira (of the island of
Madeira), Marsala, California tokay and muscatel, and similiar types
produced in many countries.
The production of sweet red wines
in Portugal has been one of that country’s most important industries
for more than two centuries. Red sweet wines, often called port, or
port-type, are also produced in Australia, California, Chile, South
Africa, and the Soviet Union. California is the principal producing
region in the United States.
At present wine makers must use
such red wine varieties as are available. Probably the Alicante
Bouschet is the poorest of these, owing to its low sugar musts, the
tendency of its wines to lose color, and to its slightly unpleasant
aroma. Carignane, Zinfandel, Mataro, and Petite Sirah are satisfactory
when picked before raisining occurs; however, Mataro is deficient in
color. The Mission and Grenache, grown in the same area, are lacking in
acid and color but are of pleasing flavor. Blends with Salvador and
Alicante Bouschet often have to be employed in order to bring up the
color. It is to be hoped that more suitable grape varieties will be
planted in the Fresno area, such as Tinta Madeira, Souzäo, Royalty, and
Rubired. The latter are two new hybrids released by the University of
California. They were created by Prof. H.P. Olmo specifically for red
sweet wine production. In the hot interior valleys of California, where
most of the sweet dessert wines are made, many varieties of red wine
grapes fail to develop sufficient color for production of port of
satisfactory tint, unless special methods of vinification are used.
There is great need for the planting of varieties of maximum red color
in these area to bring up to a desirable depth the color of ports made
from the varieties grown at present. The Salvador is widely used for
this purpose but its flavor is poor. The Souzão, Rubired and Royalty
should help supply this deficiency without the undesirable flavor.
There may be a problem of color stability with the Rubired.
Vinification of Port
The principal problem in making
port is extraction of sufficient color during a restricted period of
The grapes should be well
ripened, 23º to 25º Bailing and should be picked to eliminate moldy
fruit and handled with care to avoid bruising. They should be crushed
as soon as possible after picking. Shipping loose in bulk in gondolas
with long delays in crushing is not conducive to quality. Use of
rain-damaged grapes that have molded on the vines is also undesirable,
as such grapes give wines of poor flavor and unstable color.
Crushing and stemming are
conducted as for grapes for dry red wine. The crushed grapes are pumped
into large fermentation vats holding 10,000 gallons or more. Some
sulfur dioxide should be added during filling of the vat to give about
100 p.p.m. in the must. This will insure a cleaner fermentation, help
to stabilize the color, and assist in extraction of the color.
Early in the season a 1 or 2 per
cent starter of pure yeast is added to the crushed grapes. Later in the
season, a similar quantity of fermenting must from a vat in active
fermentation will answer the purpose but it is better to continue to
use a pure yeast culture. Flanzy reported better quality dessert wines
when the must was fermented at 59° to 68ºF compared to 86ºF. He
believed sulfur dioxide reduced the quality of the dessert wines. Both
these results need confirmation.
Frequent pumping over of must in
large vats is essential to extraction of the color. In Portugal color
extraction is accomplished by intermittent treading of the fermenting
grapes; an effective but not very aesthetic procedure.
If the grapes have good color,
and the wine maker has been lucky, his must will have attained fair
color when it has fermented to the point at which it is ready for
fortification to give a standard port of 20 × 7 composition (20 per
cent alcohol and 7° Balling) after fortification. Thus, if the original
grapes tested 24° Balling and were fermented and fortified at 13° to 20
per cent alcohol, the resulting fortified wine should be about 6°. As a
matter of fact, in this case the fermenting must would be drawn from
the vat at about 15° Balling, since there may be nearly 2° drop during
drawing off, pumping to the fortifying tank, measuring, and fortifying.
In warm regions the 15° Balling will be reached in 24 to 48 hours after
The free run will naturally not
be very deep in color. When possible the drained skins and seeds
(pomace) should be pressed, preferably in a basket or Willmes press.
However, a continuous press is generally used because of its
convenience and economy of operation. The press wine is often fortified
and is of deeper color. One can readily see the difficulty in
extracting sufficient color in such a short period of fermentation,
especially with grapes grown near Fresno, or in other hot localities.
Hence, “normal vinification” of port is usually not practicable. Other
methods are discussed in the next section.
Most San Joaquin wineries draw
the free-run colored fermenting must off at the proper stage and pump
it to the fortifying tanks. The residual pomace is then watered and
fermented for distilling. It is next passed to a Metzner still, to a
hammer mill for grinding in order to use a pomace still, to a
continuous press, or to a “scalping” apparatus (a spray of water used
to remove the alcohol). Countercurrent extraction has also been used to
recover the residual sugar. In some cases the pomace is transferred to
other tanks for completion of fermentation.
The relation between initial
Balling (or Brix) degree of the grapes, Balling of the must, and final
Balling after fortification to 20.5 per cent alcohol. Wine makers
commonly pay too little attention to fortification at the proper sugar
content. The result is that some lots are fortified too soon and more
too late. Closer attention to this table would reduce this problem.
Sparkling wines, those which
contain a visible excess of carbon dioxide are difficult to define
precisely. The present maximum for still wines is 0.277 gm. per 100 ml.
of carbon dioxide (at 60ºF.). This is equivalent to 7 lbs.
per sq. in. pressure. According to Protin most countries now
distinguish between slightly gassy wines (pétillants or perlants) from
wines with a full pressure. He reports the unofficial position of
various countries as follows:
Country Type Pressure Tem-
Austria Pétillant 1.1
Chile Sparkling 10.0
France Pétillant 3.3
Germany Pétillant 1.1
Sparkling 6. 6
Spain Pétillant 2.2
.7 Minimum ?
Switzerland Pétillant 1.1
The problem is complicated in
this country because of the higher taxes on sparkling compared to still
wines. In practice the excess carbon dioxide may originate from
fermentation of residual or added sugar, from a malo-lactic
fermentation, or from added carbon dioxide.
No classification based on method
of production is adequate to define the types of sparkling wine. The
consumer, however, is not interested in the method of production as
much as in the recognizability of the various types of sparkling wines.
Therefore, we arbitrarily define
as sparkling wines those which have more than 1.5 atmosphere pressure
at 50°F. The amount of dissolved carbon dioxide at this pressure and
temperature is approximately 3.9 gm. per liter. If the carbon dioxide
is kept at this figure the pressure at 60ºF. will be about 1.8 atm., at
70°F. 2.1 atm., and at 80°F. 2.4 atm., see Fig. 1. This is about half
the minimum suggested by the Office International de la Vigne et du Vin
for sparkling wines, 4 atm. at 68ºF.
The enologist, tax expert, and
connoisseur will need a more detailed classification of the many
different types on the market. In the classification which follows
there are some overlappings in carbon dioxide content. The source of
the carbon dioxide is thus the basis of this subdivision. In some cases
there may be no sensory test which will distinguish between the types!
carbon dioxide produced by fermentation of residual sugar from the
primary fermentation. This includes many Alsatian, German, Loire, and
Italian wines as well as the muscato amabile in California.
carbon dioxide from a malo-lactic fermentation. The Vinho Verde wines
of northern Portugal are the best representative of this type, but
there are many examples in Italy and elsewhere in Europe.
Type III. Excess
carbon dioxide from fermentation of sugar added after the process of
fermentation. Most of the sparkling wines of the world are produced by
Type IV. Excess
carbon dioxide added. This includes the so-called carbonated wines.
Carpenè distinguished four types
of fermented sparkling wines: (1) slow bottle fermentation, long aging
on yeast, disgorging, (2) same but transferred and filtered, (3) rapid
bottle fermentation, no aging on lees, transferred and filtered, and
(4) tank fermented. He stresses the importance of aging on the yeast.
He agrees with Schanderl that while the fermentation is the same in
tanks or bottles the products of methods (1) and (3) or (4) are
I Sparkling Wines
Almost any wine can be made
sparkling by stopping the fermentation before all of the must sugar has
fermented and then, later, bottling the wine. If even a few viable
yeasts are in the wine at the time of bottling, and if the sulfur
dioxide content is not excessive, the sugar will later most likely
ferment and the wine will become gassy. If the fermentation is slow at
a low even temperature the amount of yeast cells produced may be
surprisingly low. In some cases, when the yeast deposit is excessive,
the wines are treated as Type III sparkling wines and clarified in the
usual way. One reason why more wines of this type are not produced in
California is that it is most difficult to stop the fermentation with
the desired residual sugar content.
However, with the increasing
technological control of fermentation (temperature, pressure, DEPC,
depletion of amino acids, etc.) and with the generally high sugar
content of our musts it should not be difficult to produce wines by
such procedures. The addition of high, quality grape concentrate before
fermentation also offers interesting possibilities.
Sparkling wines as we know them
probably originated in this manner. It is no accident that the first
centers of sparkling wine production were in northern France. It is in
such cold regions that the fermentation is slow and incomplete. When
the temperature increased the following spring the fermentations
restarted and gassy wines resulted.
and Flavoured Wines
Vermouth consists of a fortified
wine flavoured with a characteristic mixture of herbs and spices, some
of which impart an aromatic flavor and odor and others a bitter flavor.
Two classes are recognized in the trade, the sweet or Italian-type
vermouth and the dry or French type. Dubonnet, Byrrh, Bonal, and Cap
Corse are flavored wines that are usually classed with vermouth and
will also be discussed in this chapter. In addition, there are on the
market several wines that are lightly flavored with certain herbs,
spices, fruit juices, essences, aromatics, and other natural
flavorings. They have attained considerable popularity, such as
Thunder-bird, Silver Satin, etc. Many formulas for the preparation of
each type exist. According to Joslyn the Italian or sweet vermouth
contains from 15 to 17 per cent of alcohol by volume and 12 to 19 per
cent of reducing sugar: and the French or dry vermouth usually contains
about 18 per cent of alcohol and about 4 per cent of reducing sugar.
The quantity of herbs and spices used in making the dry vermouth is
less per unit of vermouth than for the sweet; customarily about 0.5 to
0.75 oz. per gallon of the dry and 0.75 to 1 oz. per gallon of the
sweet. While vermouth is served principally “straight” in European
countries it is used in America principally in mixed drinks such as
Martini and Manhattan cocktails. Some is served mixed with sherry as a
The name is probably derived from
“Wermut,” the German word for wormwood, a frequent ingredient of
vermouth. The “w” in German is pronounced like “v” and “u” as “oo”;
hence the natural tendency to change the German spelling in English.
The German word is probably based on the alleged beneficial properties
of wines containing wormwood. The addition of wormwood to wine appears
to date from early Roman and probably early Greek times, although the
production of vermouth itself in Italy did not begin until the
eighteenth century. The quality and type of vermouth depend upon the
quality and nature of the base wine and on the kind, quality, and
amounts of the various herbs used. According to Valaer the formulas for
the European-made vermouths are closely guarded secrets, whereas there
is less secrecy among the American producers. However, Valaer occupied
a privileged position in the Internal Revenue Service. Few producers
are willing to divulge their vermouth formulas.
Before passage of the 18th
Amendment, only a limited amount of vermouth was produced in the United
States; most of that then on the market came from Italy and France.
After repeal of the amendment the demand greatly increased and
production in America rose accordingly. According to Valaer California
produced about 2,000,000 gallons of vermouth. New York State is also an
important producer of vermouth.
Flavored wines, euphemistically
and legally entitled “Special Natural Wines,” have come on the market
in the past ten years in considerable quantities. These are not
vermouths and they do not resemble the usual aperitif wines very
closely, although classed as such. They represent a new type of wine.
They usually contain the same amount of alcohol as dessert wines, 18 to
20 per cent by volume, and are sweeter than dry vermouth but not so
sweet as Italian-style sweet vermouth. The essence used for flavoring
these wines must be approved by the Alcohol and Tobacco Tax Division of
the Internal Revenue Service. The flavoring is often mild. Only small
amounts are made at present in other states. These products sell at
only slightly higher prices than dessert wines. They are served usually
“straight,” often with ice (“on the rocks”), rather than as an
ingredient of mixed drinks; in that respect differing from vermouth. A
few, for special markets, are made as unfortified wines with the same
flavor and are sold under the same name as the fortified. Recently some
of these products have resembled the standard cocktails both in name
The herbs and spices used in
vermouth are furnished in dry form and represent different parts of
various plants such as the seeds, wood, leaves, bark, or roots. Until
World War II practically all of the herbs used for vermouth production
were imported, but during the War successful attempts were made to
obtain some of the herbs from plants growing wild and to grow some of
the others in this country. Considerable quantities of these are now
grown in the United States, although most of the herbs and spices now
used are imported. Some species are obtained from the tropics and
others from the Near East, but most from European countries such as
Italy, France, and Belgium.
Information on the classification
of the more important herbs and spices used in vermouth production is
given by Pilone as bitter, aromatic, or bitter-aromatic. Bitter plants
include aloe, angelica, blessed thistle, cinchona, European centaury,
germander, lungwort, lungmoss, quassia, and rhubarb. Aromatic plants
are anise, bitter almond, cardamon, cinnamon, clove, coriander, dittany
of Crete, galingale, marjoram, nutmeg, Roman, camomile, rosemary,
summer savory, thyme, tonka bean, and vanilla bean.
The bitter-aromatic plants
include allspice, elder, elecampane, gentian, juniper, bitter orange,
sweet orange, saffron, sage, sweet flag, speedwell, wormwood (common),
wormwood (gentile), wormwood (pontico), and yarrow.
The major flavoring constituents
of the herbs and spices used in vermouth manufacture have been given by
Brevans as follows:
(such as styrol, cymene, pinene, and other terpenes)
(such as citral, citronellal, furfural, benzoic aldehyde, vanillin,
(such as methyl heptenone, carvone, luparone, thujone)
(such as alantolactone)
(such as cineole or eucalyptol)
and phenol derivatives (such as luparol, thymol, cadinone,
particularly terpenic alcohols (such as calamenol, citronellol,
borneol, anethol, eugenol, terpineol, safrol)
(such as quinine, cusparine, absotin)
(such as absinthin, gratiolin, quassin, aloin)
(such as gentinose)
(such as humulon)
(such as amyl valerianate)
acids (such as citric)
acids (such as angelic, alantolic)
The herbs and spices are usually
purchased in dried form. Therefore quality will be affected by the care
given them in harvesting and storage. They should be purchased only
from a reliable supplier who furnishes products of the highest quality.
Specimens of the same variety of plant grown under different climatic
or cultural conditions may differ markedly in character and quality.
The longer the dried products are stored before use, the poorer will be
their flavor and aroma, as these depend to a great extent on volatile
compounds that slowly evaporate during storage.
Furthermore staling of the flavor
through oxidation and other chemical reactions occur during storage.
For these reasons, the dried herbs and spices should be as fresh as
possible. During prolonged storage, insects may infest the dried
products and render them completely unfit for use in vermouth. If the
moisture content of the storage room or of the dried products during
storage is too high, molding is apt to occur with more or less damage
to quality. Fumigation at suitable intervals with methyl bromide or
odier effective fumigant is advisable to control insects if the
products are to be stored for an appreciable period.
If they are in tightly sealed
containers such as friction top cans, jars, or moisture proof plastic
bags, observation must be made occasionally to make certain that
moisture has not distilled from the product and condensed on the walls
of the package or on the product causing a local rise in moisture
content with resultant spoilage by mold. Vermouth producers should
carefully inspect all herbs offered for sale before purchase.
It is preferable to purchase the
dried plant materials in the whole form, as they can be examined more
satisfactorily than if powdered or in granular form. When the whole
plant is available it is easier to determine whether the material is
from an old or new crop. Also, the storage life of the powdered and
granular products is shorter than that of the whole materials because
volatilization of flavor and aroma is more rapid from ground material.
There seems to be an increasing
use of fluid and solid extracts, concretes, absolutes, oils, gums,
balms, resins, oleoresins, waxes, and distillates in the production of
vermouth. These may be used in amounts not to exceed the amount
reasonably required to accomplish their intended physical, nutritional
or other technical effect. Microscopic detection of impurities in or
falsification of Artemesia
other Artemesia or
with Achillea is
described by Griebel.
Considerable wine is now made in
the Pacific Coast states and in British Columbia from apples, berries,
and plums. Also some sweetened Concord grape wine similar in
composition to berry wines is made on the Pacific Coast and in several
In England and in several
European continental countries apple wine (hard cider) is produced in
important quantities. In fact, the cider of Normandy is nearly as
famous as French Burgundy or Roquefort cheese. Berry wines are made in
several European countries, particularly in Switzerland, Germany, and
the Scandinavian countries.
and Apple Wine
In Great Britain the term “cider”
means apple wine, hard cider, or fermented apple juice and nothing
else. Unfortunately in the United States it may designate either
unfermented apple juice, or the fermented, hence is ambiguous. In
France the fermented juice of the apple is cidre and
in Germany it is Apfelwein.
According to Anon, France
produced over 250 million gallons of cider, of which a considerable
proportion was distilled for apple brandy such as Calvados. Charley
reported that England at the time produced about 20 to 25 million
gallons and Germany about 6 million gallons per year. According to
Kroemer there was produced in Switzerland at that time about 12,000,000
gallons of apple cider per year. Cider and other fruit wines are also
made in most other European countries and in Canada. The U.S. Treasury
Department has reported 21.5 millions of bushels of apples and over
1,750,000 gallons of cider were used for making commercial apple wine
in the United States or a total of about 3,475,000 gallons in a single
year. This total does not include the hard cider made in the home.
for Cider in Europe
In Switzerland and Germany many
of the apple and pear trees are not grown in orchards as in America and
Canada, but are found as border trees or are scattered through the
pastures, along the roadside or in back yards. In England the trees are
usually grown in orchards with grass forming a sod between and under
the trees. The trees are usually headed quite high. In England,
Switzerland, and France a large proportion of the apple crop is of
varieties grown expressly for the production of cider rather than for
table use. Such varieties are usually high in sugar content, of medium
to low fixed acidity and higher in tannin content than table apples.
of Cider Apples
Many analyses of apples used for
cider production in various countries have been published and while all
of these cannot be reviewed here the data given in Table 1 will
illustrate fairly well the range in composition that has been observed.
Certain varieties are grown in France, Switzerland, and England for
cider making, whereas in the United States, Germany, and Canada table
varieties are usually employed.
It will be seen that some of the
French cider varieties are higher in sugar content than the apples used
in the other countries listed in the table and both the French and
British cider apples are higher in tannin content than the apples
analyzed from the United States, Germany, and Canada.
According to Kroemer cider is
made in France about as follows: the apples are stored in bins for a
few days to develop aroma. They are then washed, sorted to remove
rotten fruit, crushed and pressed in a rack and cloth press. In some
plants, according to Charley, the crushed apples are not pressed at
once but are allowed to stand for 3 to 24 hours to develop color and
flavor before pressing. The crushed fruit is allowed to drain during
this period of maceration. It is then pressed. The maceration greatly
improves the “pressability” of the crushed apples. To the juice is
added sulfur dioxide or metabisulfite to give 50 to 100 mg. of sulfur
dioxide per liter (50 to 100 p.p.m.). It is then allowed to cool to 32°
to 46°F. and settle until fairly clear through the action of natural
pectic enzymes. This practice is termed “keeving.” The juice is then
racked and allowed to ferment at 40º to 50ºF. Fermentation is slow at
this temperature, but it is believed that a low temperature during
fermentation is essential for the production of cider of best quality.
Temperature during the apple season is low and the cider producers have
no means of controlling it.
The pomace is often mixed with
water, allowed to stand several hours, and is then pressed. Sugar and
sulfur dioxide are usually added and the “juice” fermented to give a
product of rather low quality calledcidre marchand. The
resulting pomace may be watered and pressed a second time to give petite
After the primary fermentation is
completed the cider is drawn off from the yeast lees and below the cap, “chapeau
then undergoes a slow secondary fermentation for several months in
casks at about 40°F. It is then racked, bottled, and develops some
carbon dioxide pressure in the bottle. Procedure varies considerably,
however. For example, Charley reports that in some cases some of the
juice is fermented completely. It is then filtered and blended with
sweeter cider or with unfermented juice preserved at about 32°F.
Pure yeast starters may be used
in the production of French ciders in some plants, but, according to
Charley, natural fermentation is the more common procedure. Sparkling
cider is made by the bottle fermentation procedure or by the Charmat
bulk fermentation process.
Bottling and Storage of Wines
The bottling of wines is arguably
the most important of all winemaking operations since it determines the
condition in which the wine is delivered to the market. It is the
culmination of the sequence that began long before, starting with grape
development, harvesting, fermentation, and aging. Mistakes are costly
to rectify and quality control is of primary importance.
The glass bottles used for wine
are generally the 750-mL size, of clear or colored glass and in a
number of traditional shapes. Other volumes, smaller and larger, are
also used depending on the interest in further aging, the setting in
which it is likely to be consumed, and the value of the wine. The
inertness and protection offered to wines by glass bottles has been
verified by many years of usage. The most vulnerable aspect of bottled
wine is the nature of the closure or seal that is employed. For many
years corks have been unquestioned as the closure of choice due to
their compressible, relatively inert nature. However, in recent
decades, the elimination of many defects due to improved winemaking
technology has made the incidence of defects attributable to corks to
be a major problem in some wines.
The preparation of wines for
bottling, the steps involved in bottling and the aspects of their
behavior under bottle storage conditions are the subjects addressed in
this chapter. The addresses of equipment companies mentioned in this
chapter can be found in Appendix I.
The preparation of wines for
bottling involves any final adjustments of chemical composition, final
filtration, and modification of the dissolved oxygen and carbon dioxide
levels in the wines. The preparation of blends, fining, stabilization,
and adjustments of acidity should not be considered as finishing
operations and will generally have been attended to some period before
the time of bottling.
The type and style of wine will
somewhat influence whether filter pads or a membrane are to be employed
as the final filtration. The use of nominally sterile pads is widely
practiced, particularly with dry wines, while wines containing residual
sugar, or those in which the malolactic fermentation has been
prevented, will generally be membrane fitered. The assumption that dry
wines that have completed malolactic fermentation will not support
additional microbial growth is not always true in practice. While the
incidence of later microbial spoilage is lower in such cases, it is not
eliminated entirely. The continuing trend for the use of lower levels
of chemical additives and the desire to use minimal concentrations of
sulfur dioxide only enhance the recommendation of membrane filtrations
as the means to prevent unwanted microbial action in bottled wines.
Concerns about color removal from
red wines by membrane filters have no sensory basis since the material
collected on such filters has already precipitated from solution and
insoluble particles have no taste or flavor associated with them. Such
material will usually deposit in the bottle within the first months
after being bottled and the collection of it on the filter is simply
deferring the onset of such a deposit. The removal of yeast and
bacterial cells, which also have no taste contribution in themselves,
is for reasons of quality control and the assurance that the wine that
is consumed closely resembles that which was put into the bottle. The
point is, that only soluble components that can be sensed by taste
receptors on the tongue or volatile ones reaching the nasal cavity can
have a sensory impact and there is no evidence that soluble components
and small volatile molecules are significantly removed by such
The need to remove all microbes
by filtration is a far more acceptable approach to controlling unwanted
microbial activity than the chemical additive approach. The variation
in quality due to microbial effects can often be seen in wines that
have not been filtered, within the first two years after bottling.
Tasting of a series of wines from different vintages made in this style
by the same producer will generally show such changes and they are
undesirable in vintage-dated varietal wines.
The notion of stripping of wine
components by filtration has little scientific basis. While some
individuals claim to have shown this to be real, there are no panel
tests or published results to support it. It has become fashionable, in
some circles, to claim that unfiltered or unfined wines are superior,
but this has no basis in fact. There are wines that will not need to be
fined and perhaps not need to be filtered, but they are not necessarily
any better than those that have been. These arguments are generally
driven by public relations efforts that try to distinguish wineries
from one another or by wine writers who try to be controversial rather
than educational in their comments. Bottle sickness, a temporary
lowering of flavor in freshly bottled wines, appears to result from the
disturbance of an established vapor-liquid equilibrium and not from
Spoilage of Wine and Its Control
This chapter includes the
descriptions and origins of various kinds of microbiological spoilage
organisms—and the prevention of their presence and the control of their
growth it present. It is important for the winemaker to know which
spoilage has occurred in any given instance and to understand potential
spoilage problems, but obviously it is better to forestall spoilage
than to diagnose it. The taxonomic identifications of the yeasts are
given in Chapter 4, and the lactic acid bacteria in Chapter 6. For the
aerobic bacteria, the taxonomies are given at the end of this chapter.
of Microbiological Spoilage
organisms can be said to be any of those which are unwanted at a
particular place and time. Obviously, this includes those organisms
which produce off-flavors, odors, colors, or precipitates, or have the
potential to do so, under the conditions of the present and future
storage of the wine. However, this definition also includes bonafide
desirable wine yeast and bacteria when they are unwanted in a
particular wine, for example, Montrachet yeast in semidry bottled wine
in bottled wine susceptible to malolactic fermentation. To complicate
further the definition of microbiologic spoilage, one has to come to a
decision on with which flavors, odors, colors, and turbidities are to
be considered “off.” Sediments may be acceptable in aged red wines;
oxidized, aldehydic tones and brown hues are required in sherries; and
slightly reduced, sulfurous notes might be found in aged sparkling
wines. Another complication is that the distinct scents of wine from
certain geographic regions, while being expected in those wines, are
unacceptable—spoiled—in others, but have nothing to do with microbial
spoilage: for example, foxiness or muscadine flavors in wines made from
American grape varieties. Another complication is that sometimes the
acceptance of distinct odors and flavors caused by certain microbes is
controversial, as those seem to be which are be caused by Brettanomycesyeast.
And finally, one more complication to add to the list is that
winemakers may become so accustomed to their own wines that unusual
flavors and odors—unacceptable to other tasters—are unnoticed.
Winemakers are admonished habitually to taste the wines of other
producers and to have their own wines habitually tasted by sensitive
of Wine Spoilage Microorganisms
The source of microorganisms,
good and bad, in the winery comes mainly from infection, in the winery
cooperage and winery equipment, especially the equipment used at the
grape reception area and used for the transport of must or juice into
This idea flies in the face of
the assumption that most of the natural microorganisms found in wine
must arise from the vineyard. However, on sound, healthy, and intact
grapes, the berry surface is not much different than that which would
be found on any inert surface outdoors.
It is true that the wild yeasts,
such as Kloeckera and Hansenula, are
exceptional; they are found on healthy berries—near the pedicel. Their
presence may be related to the expectation that the grape skin surface
at this region seems to allow some contact with the nutrients within.
These nutrients, having a high content of sugars and a low pH, are
selectively attractive to these yeasts. Why the presence of a
correspondingly high concentration of wine yeast, that is, strains of Saccharomyces
also not found is not clear.
Of course not all of the grapes
are healthy; breaks in the skin arise from normal conditions such as
strong winds brushing berries against each other or against the woody
parts of the vine. These breaks in the skin then allow unrestricted
growth of all sorts of microorganisms. Other sources of breakage of the
skins are bird pecks, hail, or even heavy rainstorms. So it could be
expected that even under the best conditions of berry ripening, a
substantial portion of the berries would give some exposure of the
contents and allow enough growth of all sorts of organisms giving an
incipient infection in the juice or must when it arrives inside the
The description given several
years ago of the origins of Brettanomyces spoilage
in some wines in South Africa can serve as the scenario for the origins
of many kinds of infections, including those of both good and bad wine
microbes. In the Brettanomyces work
it was discovered that during the crushing and destemming operations
there was some buildup of the infecting organisms in the pools of juice
associated with this equipment. Acceptance of only the most healthy
fruit and interruption of the crushing operations and washing of the
equipment from time to time would tend to minimize this buildup.
However, as mentioned above, even the most healthy fruit is not
completely devoid of all unwanted organisms.
Furthermore, the washing
operations, if not done thoroughly enough, might only aggravate the
situation. That is, the dilution of the grape juice brings about a
lowered concentration of sugar and an increased pH, and an
encouragement of growth of various yeast and bacteria.
This is especially true when
pools of diluted grape juice are left standing for an extended time,
such as overnight. To continue with the scenario, the diluted pools of
juice can serve as ideal starter culture media for all sorts of
microorganisms Contamination from them eventually reaches into the
winery, into fermenting juice and eventually into stored wine. When
this sort of starter culture comes in contact with undiluted juice and
wine, then only those that thrive on anaerobic conditions at low pH and
probably cooler temperature, that is to say, the wine-related
microorganisms, will survive. And if nutrients are available, they will
grow. The conclusion of the scenario is that if even a single, viable
organism under these conditions finds its way into a demijohn, barrel,
or tank of wine, with enough time, this organism can multiply to
This same scenario can apply to
all sorts of wine spoilage organisms, and even to desirable wine
organisms, including wine strains of Saccharomyces
coveted malolactic bacteria.
In the Brettanomyces studies,
the proper prevention was found to be in very thorough cleaning of the
crushing equipment and of the piping or hoses from the reception area
into the winery, including judicious use of sulfur dioxide to aid in
sanitizing. This means that every several hours, there should be a
complete halt to the operations and thorough enough washings of the
equipment to leave no diluted pools of juice. The washing operations
needed to be especially thorough at the end of the day, and at the
beginning of the next. Where continuous crushing is done, very thorough
washing operations should be made several times during each 24-hour
period. Such washing is not a sterilization procedure, but helps
prevent buildup of contaminants.
We have found that the piping or
hoses transporting the juice and must into the winery can be very
susceptible to accumulation of contaminating microbes. In one winery
with an especially difficult situation withBrettanomyces infection,
the piping was underground and made a right angle from the reception to
the winery. Over the years, the bend in the piping had allowed a
collection of a large mass of material, which sheltered all sorts of
contaminants, some seemingly carrying over from season to season. The
contamination problem was solved only by unearthing and replacing the
piping, and redirecting it to give only gentle curvatures.
: Reducing Sugars
Carbohydrates are polyhydroxy
aldehydes, ketones, and their derivatives, composed of carbon,
hydrogen, and oxygen in the ratio Cn(H2O)n. On a molecular basis,
carbohydrates exist as monosaccharides, such as glucose and fructose,
disaccharides, such as sucrose, and long-chained forms, the
polysaccharides. Polysaccbarides may be hydrolyzed to di-and
trisaccharides and, ultimately, to monosaccharides. Examples of
polysaccharides that are of potential importance to the winemaker
include pectin, and starch as well as the alginates used in fining.
Other compounds that qualify as carbohydrates include deoxy- and amino
sugars, sugar alcohols, and acids.
To the enologist, the most
important carbohydrates are the six-carbon sugars, glucose and
fructose, utilized by yeast in alcoholic fermentation. These two sugars
also are referred to as reducing sugars. Reducing sugars may be
operationally described as those sugars containing functional groups
capable of being oxidized and, in turn, bringing about reduction of
other components under specific analysis conditions (copper, as Cu II,
used in their analysis). Thus, certain pentoses also are classified as
reducing sugars, even though they are unfermentable by wine yeasts.
Glucose and fructose may be
differentiated on the basis of the location of their respective
functional carbonyl group. As seen in Fig. 1, the carbonyl group of
glucose is located on the first carbon and thus is defined as an
aldo-group. In fructose, the carbonyl function is located on the second
carbon; thus fructose is an example of a keto-sugar. Intramolecular
bond angles create molecular structures for these sugars so that they
normally do not exist as straight-chained molecules but rather in
cyclic configurations called hemiacetals (glucose) or hemiketals
Cyclization does not involve the
gain for loss of atoms by the sugar molecule. Thus the straight-chained
and cyclic forms are isomers, with the cyclic form representing the
more important (prevalent) configuration. Glucose, for example, exists
both in solution and in crystalline form almost entirely as the cyclic
hemiacetal. The fact that sugars display most of the reactions
considered typical of aldehydes is the result of an equilibrium
established between the open-chained and cyclic configurations present
Cyclization introduces another
structural consideration into the chemistry of sugars. In solution,
sugars can occur in rings composed of four carbons and one oxygen or
five carbons and one oxygen. The former is termed a furanose ring and
the latter a pyranose ring (see Fig. 1).
In grapes, glucose and fructose
occur in approximately equal concentrations, each contributing
approximately 10 g/100 g to juice. The disaccharide sucrose is the
third most abundant sugar, accounting for 0.2 to 1.0 g/100 g. Although
glucose and fructose normally are present in a ratio of
1 : 1 in the mature fruit, the proportions may vary
significantly. Climatic conditions during the growing season may affect
the glucose-fructose ratio; Kliewer found that it decreased in warmer
seasons and increased during colder periods. Amerine reported ratios
ranging from 0.71 to 1.45 in California’s 1955 vintage, whereas Kliewer
cited ratios of 0.74 to 1.05 in Vitis
varieties. During maturation, the ratio of glucose to fructose usually
In their review of wine
microbiology, Kunkee cite differential utilization of glucose and
fructose by yeast. At must reducing sugar levels of 17 to 20%, glucose
was reported to be fermented faster, whereas at higher reducing sugar
levels (> 25%) the rate of fructose utilization was greater.
Between 20 and 25% reducing sugar levels, both sugars fermented equally
well. Peynaud notes that the ratio of glucose to fructose declines
during fermentation from near 0.95 at the start to 0.25 near the end of
fermentation. Thus, it,can be seen that fructose usually is present in
greater amounts than glucose. As fructose is nearly twice as sweet as
glucose, the cited ratios explain the observation that wines sweetened
with grape concentrate or mute appear less sweet than wines with the
reducing sugar produced by arresting the fermentation.
Reducing sugar analyses play
multiple roles in wine processing considerations. The winemaker needs
to know the quantity of fermentable sugar remaining in the wine to
determine if the fermentation is complete. This may be important so
that provision can be made for dealing with microbial stability as well
as potential blend preparations. Additionally, monitoring the
fermentable sugar content in pomace, distilling material, and so on, is
of concern in overall plant efficiency. Traditionally, one attempts to
obtain a measure of the residual fermentable sugar by analysing for all
remaining reducing sugars. Thus, although one might expect “dry” table
wines to have close to zero residual sugar upon completion of fermentation,
typical analytical reducing sugar results are higher because of the
contributions of nonfermentable pentoses.
As a result, dry wines
traditionally have been defined as having reducing sugar levels of 2.0
g/L (0.2%) or less. In contrast, McCloskey defines the sugar content of
a “dry” wine as ranging from 0.15 to 1.5 g/L (when determined by
enzymatic assay specific for glucose and fructose). Because the primary
reducing sugar content in a dry wine is attributed to pentoses which
are not fermentable by yeast, a dry wine (< 0.02% reducing
sugar) generally is considered stable with respect to yeast
The disaccharide sucrose serves
as an important energy storage compound in most plants and vegetables.
Although sucrose itself is unfermentable, the products of its
hydrolysis, glucose and fructose, are utilized readily. In the case of
grapes, upon translocation to the berry, hydrolysis by invertase
enzymes yields glucose and fructose. Thus, sucrose levels in grape
berries, at maturity, range from 0.2 to 1 %. Because yeasts produce
their own invertase enzyme, chaptelization of sugar-deficient musts
with sucrose does not cause problems relative to fermentability.
and Biochemistry of Ethanol Fermentation
The transformation of grape juice
into wine is essentially a microbial process. As such, it is important
for the enologist to have an understanding of yeast and fermentation
biochemistry as the fundamental basis of the winemaking profession. The
alcoholic fermentation, the conversion of the principal grape sugars
glucose and fructose to ethanol and carbon dioxide, is conducted by
yeasts of the genus Saccharomyces,generally
by S. cerevisiae and S. bayanus. The
current use of the old term bayanus for
the yeast closely related to S. cerevisiae is
controversial but we expect bayanus to
become once more an accepted appellation.
Origins, and Identification of Wine-Related Yeasts
of Wine-Related Yeasts
By wine-related we mean those
yeasts which have been found on grapes or in vineyards; in wines, table
or dessert, sound or spoiled; or associated with wineries or winery
equipment. Comprehensive listings of these organisms have been
published. The taxonomies of the wine-related yeast genera grapes in
this section are based on these listings, and include some 18
genera—the more obscure and rare being omitted.
Wild yeasts are those non-Saccharomyces fermentative
yeasts found on grapes, which may take part, if not hindered, in wine
fermentations, at least at the outset, and include Kloeckera,
Hanseniaspora, Debaryomyces, Hansenula, and Metschnikowia. Wine
yeasts then are the many strains of Saccharomyces, which
not only can carry out a complete fermentation of grape juice, or other
high sugar-containing medium, but also provide the fermented product
with pleasant, winelike flavors and odors. Species of Schizosaccharomyces can
also completely ferment grape juice, and in special cases they have
been suggested as wine yeast substitutes of Saccharomyces: however,
more often than not, the fermentations produced by Schizosaccha-omyces are
unappealing. Using the above subjective definition for wine yeast,
several Other genera could also be included: Brettanomyces,
Dekkera, and Zygosaccharomyces.
We make these distinctions
between wild yeasts and wine yeasts for convenience; it would be just
as sensible to call “wild yeasts” those yeasts which have never been
isolated and grown in vitro and placed in laboratory storage
conditions, and wine yeasts could mean all wine-related yeasts.
Furthermore, we are not using the term wild
the genetically correct way to indicate the parent strain from which
various mutant strains have been derived.
of Wine-Related Yeast
The presence of many yeast genera
on grapes in the vineyard at ripeness has long been established. Indeed
electron scan microphotographs of the surface of grape skins showing
distinct and intact bipolar budding yeast have been made. The presence
of multilateral budding wine yeasts also on grapes has been supposed
for as long. There are many reports of the presence of strains of S.
grape skins, but generally these have either been vague as to actual
numbers or have been the result of enrichment culturing. For enrichment
culturing, whole berries, or skin washings, are used to inoculate a
selective nutrient broth. The presence of wine yeast in the incubated
medium indicates that at least one viable yeast cell was initially
present. These reasonable assumptions have lead to extensive written
and oral speculations, anecdotally based, on the importance of both
wild yeasts and wine yeasts found on the grapes with respect to
subsequent natural fermentations.
It has been advocated by others
that the distinct characteristics of wines from various
long-established, and often famous, wineries come from the yeast in
residence in the vineyards associated with wineries. The wild yeasts
are thought to provide their own special flavor nuances before being
overwhelmed by the wine yeasts, and the wine yeasts add their own
distinctive flavor notes. Both of these postures are now generally
discredited, with some possible exceptions.
Alternatively there has been a
renewal of the suggestion that perhaps there are no wine yeasts on the
grapes at all, and that the inoculations in a natural fermentation come
from yeast indigenous in the winery. It is true that most of the
evidence for wine yeast actually present on the skins of ripe berries
comes from enrichment culture studies. Furthermore, we have
demonstrated long delays in commencement of fermentations of juice from
grapes prepared outside the winery, whereas when the juices from the
same grapes were prepared (stemmed and crushed) in the winery, there
was little delay in the start of the fermentation. The question arises,
how does the yeast become resident in the winery? The answer is
essentially the same as for the infections of wineries by spoilage
yeast and bacteria, but it is based on the simple idea that whenever
there is an environment favorable enough for the survival or growth of
a microorganism, given enough time, the population will become
We have demonstrated the presence
of strains of S. cerevisiae on
skins of ripe grapes without resorting to enrichment culturing. The
main difficulty with this kind of demonstration is that the number of
wine yeasts cells is so low that the grape skins must themselves be
applied directly to the solid nutrient medium; or a minimal volume of
liquid must be used to wash the surface of the grapes, and then plated,
that is, spread directly onto solid medium. The problem comes from the
great susceptibility of the plating method to contamination by molds,
which are fast growing. The growth of a single mold cell on a plate can
overrun any other colonies within a day or two. For the demonstration
of the presence of wild yeast, such as Kloeckera or Hansenula, which
are here in much higher numbers, samples from the grapes can be greatly
diluted so that the chance of getting even a single mold cell on a
plate is substantially diminished.
Chemicals such as biphenyl and
thymol have been touted as useful for prevention on mold growth under
these conditions, but we have not found them to be effective. Rather,
we have developed a selective medium, containing sorbate and ethanol
which, when incubated mildly anaerobically, will (after some two weeks’
delay) allow the formation of wine yeast colonies. Further
identification needs to be made because this method could also allow,
for the growth of Brettanomyces (and
Schizosaccharomyces, and Zygosaccharomyces.
of Wine-Related Yeasts
It is important to be able to
identify the genus and species of wine-related yeasts in order to
compare them and their contribution to a given wine or winery, to
assess problems arising during fermentation and microbial spoilage, and
to evaluate different yeasts as inocula.
Compounds and Wine Color
Variations in wine types and
styles are largely due to the concentration and composition of wine
phenols. From the vineyard to production and aging, fine wines can be
viewed in terms of management of phenolic compounds. Phenols are
responsible for red wine color, astringency, and bitterness; they
contribute to the offactory profile; serve as important oxygen
reservoirs and as substrates for browning reactions.
Grape and Wine Phenols
Grapes and wine contain a large
array of phenolic compounds derived from the basic structure of phenol
(hydroxybenzene). Representative structures of the major classes are
presented in Fig. 1. Two distinct groups occur in grapes and wine: the
nonflavonoid and flavonoid phenols. The total phenol content of wine is
less than that present in fruit. Traditional fermentation following
crushing and destemming leads to a maximal extraction of up to 60%.
Microbial activity may lead to increases in the concentrations of
certain phenols. Fermenting and/or storage in oak provides additional
sources of phenolics. Singleton reported the average values for
phenolic fractions and total phenols (see Table 1). Due to the broad
chemical diversity of phenolic compounds, total phenols in must and
wines are usually presented in arbitrary units of a phenolic standard
such as amount of gallic acid necessary to produce the same analytical
response or gallic acid equivalents (GAE). As a result of changes in
winemaking style, wines produced in the Unites States tend to be lower
in tannin and with more supple tannins.
In wines not stored in oak, the
primary nonflavonoid phenols are derivatives of hydroxycinnamic and
hydroxybenzoic acids, the most numerous of which are esterified to
sugars, organic acids, or alcohols. The nonflavonoid component arises
principally from juice extraction and secondarily from
post-fermentation activity, including exposure to oak coopperage.
The levels of benzoic acid and
its derivatives in red wines range from 50 to 100 mg/L and in whites
from 1 to 5 mg/L. Salicylic acid is present at levels of more than 10
mg/L and other derivatives are present in only trace amounts.
Most nonflavonoids are present at
levels below their individual sensory threshold; however, collectively
members of the group may contribute to bitterness and harshness.
Content of Juice
The phenol content of juice is
largely nonflavonoid. The levels of nonflavonoid phenols are relatively
constant in red and white wines, because of their extractability from
grape pulp. The major source of nonflavonoids from grape solids is the
hydrolysis products of anthocyanins, hydroxycinnamic acyl groups.
Hydroxycinnamate derivatives comprise the majority of this class of
phenolics in both white and red wines. These compounds are present in
juice and wine as the free acids and ethyl esters and in the form of
tartrate or tartrate-glucose esters. Hydroxycinnamates serve as the
primary substrate for polyphenol oxidase activity.
Derived from Fermentation and Extraction from Oak
During alcoholic fermentation,
slow (incomplete) hydrolysis of nonflavonoid esters occurs, resulting
in free acid and ester forms. Caftaric and similarly bound or acylated
phenols are hydrolyzed to varying degrees, yielding the corresponding
free cinnamic acids. Somers reported that fermentation caused total
hydroxycinnamates to decrease by nearly 20% due to adsorption by
yeasts. Cinnamic acid may be involved in the formation of microbially
produced compounds such as 4-ethylcatechol. This transformation
involves decarboxylation of the acid to yield 4-vinyl-catechol and
subsequent reduction to 4-ethylcatechol. Similar microbially induced
transformation of benzoic, shikimic, or quinic acids to yield catechol
and protocatechuic acid has been reported. Ethyl phenols are important
sensory compounds of red wines.
Some produced by Brettanonyces/Dekkera, are
responsible for phenolic or leathery off odors. Analysis of 4-ethyl
phenol can be used as a marker for Brettanonyces/Dekkera.
Tyrosol is produced by yeast from tyrosine during fermentation and is
the only phenolic compound produced in significant amounts from
Component Arising from Oak
In wines not exposed to oak
cooperage, the nonflavonoid phenol fraction is about the same as in the
juice from which the wine was produced. Phenols extracted from oak are
present almost entirely as hydrolyzable nonflavonoids. Vanillin,
sinapaldehyde, coniferaldehyde, and syringaldehyde are reported to be
the major species present in barrel-aged wines. (See section on Oak
Much of the structure and color
in wine is due to flavonoids that are found in skins, seeds, and pulp
of the fruit. The base structure (aglycone) of flavonoids consists of
two aromatic rings, A and B, joined via a pyran ring. (The base
structure and standard numbering system are seen in Fig. 2.) Changes in
the oxidation state result from variations in hydrogen, hydroxyl, and
ketone groups associated with carbons 2, 3, and 4 leading to different
members of the family.
Flavonoids may exist free or
polymerized to other flavonoids, sugars, nonflavonoids, or a
combination of these. Those esterified to nonflavonoids or sugars are
referred to as acyl and glycoside derivatives, respectively.
Polymerization of catechin and leucoanthocyanidin flavonoids produces
the procyanidin class of polymers. Their classification is based on the
nature of the flavonoid monomers, bonding, esterification to other
compounds, or functional properties. The most common functional class
of procyanidins is the condensed tannins.
Monomeric flavonoids react to
yield dimeric and larger forms, resulting in an array of heterogeneous
structures. Polymeric flavonoids make up the major fraction of total
phenolics found in all stages of winemaking. Polymerization, either
oxidative or nonoxidative, yields tannins and condensed tannins,
respectively. Further polymerization may eventually lead to
Processing protocol will
significantly affect the phenolic composition of wine. Flavonoids are
derived primarily from the seeds, skin, and stems of grapes.
Anthocyanins and flavonols (Fig. 2) are extracted mainly from the
skins, and catechins and leucoanthocyanins from the seeds and stems.
Increasing the skin contact time and temperature and the extent of
berry breakage increases the flavonoid content. The distribution of
phenols in a red wine with 1,400 mg/L (GAE) is seen in Table 2.
Flavonoid phenols usually account for 80 to 90% of the phenolic content
of conventionally produced red wines and about 25% of the total in
whites crushed but without skin contact.
Carbon Dioxide and Ascorbic Acid
Oxygen contact with must and wine
is a concern to the winemaker throughout the winemaking process. In
some instances (e.g. in juice processing, during barrel aging, etc.),
selected and controlled exposure to oxygen may play an important and
beneficial role in wine quality. In situations such as bottling, oxygen
levels should be as low as possible to prevent premature deterioration.
Since the early 1970s, results of
research as well as commercial wine production have suggested that
limited oxygen contact of the must prior to fermentation may not be as
detrimental as once thought. Studies indicate that oxidative browning
occurring in juice may be reversed during fermentation. Oxidative
polymerization of phenols in white juice reduces the phenolic content
of the subsequent wine and aids in buffering the wine against further
Derivatives of hydroxycinnamates
are the primary phenols responsible for enzymatic browning in juice.
Utilizing these substrates, polyphenoloxidases catalyze oxidation
leading to browning. S-Glutathionyl caftaric acid is the major product
formed, and is itself resistant to further attack by polyphenoloxidases
and browning. The rate and extent of browning depend on the
concentration of hydroxycinnamates. However, the reaction is intimately
related to all the conditions existing in the must and fermenting wine
(pH, oxygen levels, increasing alcohol content, etc.).
There is mounting general concern
regarding medical ramifications of sulfur dioxide usage. As a result,
emphasis has been directed toward reducing use levels and, eventually,
eliminating sulfur dioxide in processing altogether. In addition to
medical concerns, proponents of sulfite elimination in wine processing
point to several other areas of concern relative to its use. (1) Total
phenolics are higher in musts receiving prefermentation additions of
sulfur dioxide. (2) sulfur dioxide reacts rapidly with several
compounds present in juice and wine, chief among them acetaldehyde. The
latter reaction product is rather stable and has no or questionable
activity in prevention of oxidation or inhibition of most
Further, formation of the
addition compound reduces the levels of free molecular sulfur dioxide
present, thereby creating a need for further additions in order to
achieve the desired levels of molecular sulfur dioxide needed for
microbiological and oxidative stability. Because of the reactivity of SO2 and
acetaldehyde, the timing of sulfite additions has a major influence on
final concentrations of both components in wine. Wines produced from
sulfited juice, or which have had sulfite additions made during
fermentation, have significantly higher levels of acetaldehyde than do
those produced with no added sulfite. (3) Where a malolactic
fermentation is considered desirable, high levels (> 50 mg/L) of
total sulfur dioxide used in juice processing may inhibit the potential
for microbial growth.
To reduce the levels of sulfur
dioxide used while maintaining high standards of wine quality, careful
control of virtually every facet of wine production is necessary, from
the vineyard to the bottled product. Concern regarding the potential
for excessive oxidative degradation begins in the vineyard. Relevant
factors include grape variety, climatological conditions, harvest
maturity, and fruit temperature at harvest, in transport, and during
Grape chemistry and integrity
also play roles in oxidation. High-pH musts and wines tend to oxidize
at a faster rate than low-pH lots. Winemakers forced to deal with
mold-damaged fruit expect to observe more oxidation than is seen in
must produced from sound fruit. In these cases, the use of higher
levels of sulfur dioxide may be needed to control further deterioration
by bacteria and wild yeast. In some instances, microbially produced
oxidases may not be inhibited by sulfur dioxide used at reasonable
levels. During its growth, Botrytis
laccase that is relatively insensitive to sulfur dioxide and alcohol.
One technique for dealing with oxidase activity employs prefermentation
juice fining. Although
a variety of enzymes are present in sound fruit, fermentation and
processing reduce their activity substantially.
Polyphenoloxidase activity in
wine is not considered to play a major role in further oxidative
degradation, although laccase activity may continue. Browning of wines
thus is mainly a function of nonenzymatic oxidation of phenolic
The color of wine is one of its
most important characteristics, so a departure from what is generally
accepted as the “normal” color of a wine can be a serious problem. The
potential for color changes leading to browning in wines may be closely
tied to grape variety, because of differences in concentration and
activity of polyphenoloxidase. Grapes grown in warmer regions tend to
darken faster than the same variety grown in cooler areas. Also,
maturity seems to affect the tendency toward browning. It would appear
that controlled oxygen contact with the must plays an important, and
probably beneficial, role in wine quality.